Coated abrasive article and the method of making the same



May 6, 1952 F. J. TONE ET AL COATED ABRASIVE ARTICLE AND THE METHOD OF MAKING THE SAME Original Filed MaylS, 1936 mmmammmmam am'fiwmt INVENTORS. FRAN K J. TONE MARTIN HARRY C.

ATTORNEY.

Patented May 6, 19.52

COATED ABRASIVE ARTICLE AND THE METHOD or MAKING THE SAME Frank J. Tone and Harry C. Martin, Niagara Falls, N. Y., assignors to The Carborundum Company, Niagara Falls, N. Y.,'aa corporation of Delaware Original application .May 13, 1936, Serial No. 79,549. Divided and this application July 15, 1940, Serial No. 345,596

9 Claims.

This invention relates to granular coated products and the method of manufacturing the same; and more specifically to abrasive coated products of a somewhat flexible character, such as belts, discs, and the like.

This application is a division of our copendin application, Serial No. 79,549, filed May 13, 1936, upon which U. S. Patent No. 2,252,587 was granted August 12, 1941.

Abrasive coated flexible discs, which are one of the products for which our invention is particularly well adapted, have heretofore ordinarily been made by coating a suitable backing, such as vulcanized fibre or vulcanized fibre and cloth, with abrasive granules attached to the backing by means of glue. Articles of this type are used for a variety of purposes, such as polishing wood, metal, or lacquered surfaces. For such purposes as these, which might be termed smoothing, a fine grit abrasive would be indicated; but for what might be termed more strictly abrasive pur poses, in which the primary object is to remove material rather than to smooth an article, coarse granules would be used. Although our invention is by no means restricted to abrasive articles carrying coarse grits, it is especially well adapted for improving this type of article and lengthening its useful service.

One use to which discs made by our improved-- process have been satisfactorily applied is in the removal of the excess material applied in making welds; and it has been found, for example, that discs made in accordance with our-invention have at least from two to three times the life of the discs made in accordance with the methods here tofore known.

In order to facilitate understanding of the invention we have illustrated it by a number of drawings wherein:

Figure 1 is a side elevation of a part of a coinpleted article made in accordance with the invention;

Figure 2 is a plan view of a completed article embodying one modification of the invention;

Figure 3 is a side elevation of a backing coated with binder, as used in carrying out the invention; and

Figure 4 is an enlarged sectional view of a coated abrasive grain of the class used in the invention.

Referring to the drawings, the articles comprise a backing I having abrasive grains 2,at tached thereto by a binder 3. The binder of the completed articles comprise the coating 4, which is applied directly to the backing l' (as illustrated in Fig. '3) and the coating 5 which is first applied 2 to the abrasive grains 2 (as shown in Fig. 4) and is caused to flow to the backing and unite with the coating 4 when the article is given a suitable heat-treatment as will be fully described hereinafter.

In carrying out one form of our invention, we may use an intermediate product which has been found to be valuablein the production of bonded abrasive products, such as wheels or stones. The method of manufacturing this intermediate prodnot and a method of making bonded abrasives from it are disclosed and claimed in a United States Patent No. 2,010,873.

For the purpose of fully explaining our invention, we will now discuss a method of forming this intermediate product which we have found to be particularly well suited for use in our invention.

In making this intermediate product, we first coat abrasive granules with a suitable plasticizing medium, such as a liquid heat-hardenable resin, or other resin solvent. The grain coated with the plasticizing. medium is then admixed with a dry powdered heat-hardenable resin, such as a phenolic condensation product in the fusible and soluble condition. By properly adjusting the proportions of the plasticizing medium and powdered resin, as by applying 3 to 4 parts of powdered resin to about 25 to 50 parts of grain which has been wetted by one part of plasticizing medium it is possible to prepare in this way a product which consists of individually coated abrasive granules which are dry and non-tacky at ordinary temperatures but which are sufiiciently cohesive so that upon pressing they can be formed into a shaped article. If, now, the coated granules are passed through a suitable screen, they can be separated into individual grains and spread on a plate, belt or the like in isolated condition.

If these coated granules are passed through an oven, the temperature of which is about 350 to 375 F., and are exposed to this heat for a period of about two to ten minutes, while being maintained in an isolated condition such that substantially none of the granules are touching each other, it will be found that the resin has dissolved, or at least has liquified and merged with the plasticizing medium to form a substantially homogeneous coating of resin surrounding and encapsulating the individual abrasive grains. Upon cooling, the resin coatings are sufficiently hard and non-cohesive so that there is no tendency of the grains to asglomerate.

In making a coated product with these granules in accordance with one of the methods of this invention, a coating of a suitable liquid heathardenable resin, such as a normally liquid phenolic condensation product formed by reacting a phenol and an aldehyde and arresting the reaction when the product is liquid at ordinary room temperatures, is first applied to a backing such as a very thin sheet of spring steel. The coated granules, encapsulated with resin as just described, are then sprinkled onto the liquid resin and the article is heated to harden the liquid resin and the resin coatings on the granules. After such a treatment it will be found that the granules will be attached to the heat-hardened (previously liquid) resin adhesive by reason of the solubility of the coating resin on the grains in the liquid resin adhesive, which causes the two resins to mutually fuse and weld when the article is heated to cure the bond. At the same time, the coating resin which was applied to the grain tends to fiow to a small extent to form a mounting for the coarse granules in the form of a concentration of the resin at the base of each granule. As a result of this condition, the grain is especially well attached to the backing, and is very resistant to removal by stresses applied to it during service.

A modification of the process just described involves the omission of the oven treatment in the course of the production of the coated grains so that the grains are encapsulated with pulverized resin adhesively attached to the individual grains. The other steps followed in producing the coated grains will be the same in all material respect as those above described. Although coated grain produced by this modified method can not be handled so satisfactorily from a manufacturing standpoint, the abrasive articles themselves produced in accordance with this modification are quite satisfactory. The omission of the oven treatment leaves the resin coating on the abrasive grains in a somewhat fragile condition, as the resin is not firmly attached to the grains and therefore tends to become dislodged when the grains are applied to the backing. Although considerably more care must be used, for this reason, in carrying out this modified process than in carrying out the preferred process, articles made in accordance therewith are substantially as long-lived as those made by the preferred process.

Another process of coating the grain comprises heating a mixture of abrasive grain and normally solid resin in an oven and stirring until the resin melts and coats the grain. The mass of coated grain is then cooled and passed through a crusher whose rolls are spaced somewhat more than the maximum particle size so as to break up the mass into individual coated grains without fracturing the grains.

We will now give a number of specific examples to illustrate our invention, it being understood that the examples are illustrative only and not limitative.

Example 1.-The backing selected was a disk of Swedish spring steel 9 diameter, .015" thick and provided with a hole at its center for the purpose of mounting. On this disk was applied a coating in the form of a band or ring 2" wide extending from the periphery of the disk toward its center. 5 grams of coating were used, the coating consisting of a mixture of 60 parts of Bakelite liquid resin No. 1372 and 40 parts of pulverized fiint. To the coated portion of the disk were applied 27 grams of coated grain consisting of No. 24 grit fused alumina coated with resin in the proportions of 82 parts of grains to 18 parts of bond. This gives a substantially single layer about one grain deep.

The coated grains were prepared by first moistening the surface of 82 parts of grain with 3 parts of a normally liquid phenol-aldehyde condensation product and then dusting on a mixture of 6 parts of pulverized flint and 9 parts of a powdered heat-hardenable phenolic condensation product resin in the so-called A stage. The coated grains were scattered in separated condition on a belt and were then exposed to a temperature of 375 F. for 6 minutes to melt the resin. When cooled the coated grains formed a loose non-coherent mass which was sprinkled on the liquid resin coated backing.

The disk to which first the liquid resin had been applied and then the coated grain, was next dried for 24 hours at F. and then baked for 6 hours at 300 F. This disk had a life of 27 minutes, removing 285 grams of metal, as compared to a life of 9 minutes and grams of metal removed by a disk in which the grain was bonded with glue, in accordance with the previously known method.

Example 2.-To a disk coated with a mixture of liquid resin and flint as described in Example l was applied 27 grams of coated grain. The coated grains were prepared from 81 parts of No. 24 grit fused alumina and 19 parts of an A stage phenol-formaldehyde resin. The 81 parts of grain were coated by first moistening the surfaces of the grain with 3 parts of a normally liquid phenol-aldehyde condensation prodnot and then dusting the same with a mixture of 6 parts of pulverized flint and 10 parts of a powdered heat-hardenable phenolic condensation product resin in the A stage. To the disk coated as above described was applied the 27 grams of coated grain; and the article was then dried for 24 hours at 125 F. after which it was baked for 6 hours at 300 F. This disk had a life of 2'7 minutes and removed 289 grams of metal.

Example 3.A file was made by coating a piece of wood 1" square and 12" long with normally liquid phenolic resin and No. 16 grit fused alumina prepared in accordance with the method described under Example 1. The resin was cured by first drying the article for 14 hours at F and baking for 12 hours at 250 F.

Example 4.-To a disk coated with a mixture of liquid resin and flint as described in Example 1 were applied 27 grams of coated abrasive grain. This coated grain consisted of No. 24 grit fused alumina coated with melted resin in the proportion of 81 parts of grain to 19 parts of bond. The 81 parts of grain were coated by placing the same together with 13 parts of a heat-hardenable phenolic condensation product resin in the A stage and 6 parts of pulverized flint in an oven heated to 375 F. After a sufficient period of heating to melt the resin, during which period the mixture was stirred, the mass was removed from the oven and cooled. The hardened mass was then passed through a crusher whose rolls were spaced sufficiently to permit the largest granules of the No. 24 grit to pass. The coated disk, to which these coated grains had been applied, was next dried for 24 hours at 125 F. and then baked for 6 hours at 300 F. This disk had a life of 21 minutes and removed 196 grams of metal.

The coatings of adhesive and abrasive grains may be applied to the backing in any convenient manner. Where abrasive coated articles are made on backings which are not obtainable in the form of continuous webs, it is convenient to brush or spray the liquid onto the backing and then to apply the coated abrasive grains in an excess and remove the excess grain as by inverting the article. Where the backing is obtainable as a web the process may be conveniently carried out in a conventional abrasive coating machine such as is commonly employed in the manufacture of abrasive paper or cloth, usually referred to as sandpaper. As is well known, in such machines the web of backing material is continuously passed between a pair of revolving rolls, one of which is partially immersed in a vat of adhesive, thereby coating one side of the backing with the liquid adhesive, and an excess of abrasive grain is fed onto the adhesive coated side of the moving web. The excess abrasive grain is then removed as by passing the coated web downwardly so that unattached grains fall off the web.

We have also applied our process to an improved method of coating which is described and claimed in copending application Serial No. 66,627, filed March 2, 1936, wherein a backing is first coated with a liquid resinous adhesive and partially coated with abrasive grains to cover somewhere about 20% of the surface of the backing and the partially coated web is then additionally coated with a liquid resinous adhesive and resin-coated grains to substantially completely cover the backing and to form clusters of grains about the grains first applied to the backing.

Our method is therefore adapted to be used in any of the methods used for forming thin layers of abrasive grains wherein a large proportion of the grains are attached directly to a backing member, in distinction to molded articles wherein articles are formed by compacting a mass of grains so as to get a multi-layered article several grains thick. In describing and claiming our invention we have used the expression substantially single layer to mean a layer such as is obtainable by coating methods wherein a major proportion of the grains are attached directly to the backing, as distinguished from multi-layered articles such as are obtainable by pressing or otherwise compacting as in a mold, even though the coating of our articles may be more than one grain deep in places.

Although, as previously stated, our invention has been found to be especially suited for the production of flexible disks, it is equally well adapted to the manufacture of all forms of abrasive coated articles carrying a substantially single layer of abrasive grains, such as abrasive belts or coated fabrics of the nature of sandpaper. As described in Example 3, we have also found it useful, for example, in the manufacture of files and like articles which may, of course, be made on a more rigid base such as wood or rigid metal.

The substantially unplasticized synthetic resins employed in our invention, and particularly the phenol-aldehyde condensations referred to in the specific examples, are cured by the time-temperature conditions specified in the examples to the state where they are inflexible, water-resistant and hard. The cured bonds holds the grains rigidly in place, have tensile strengths substantially above 6,000 pounds per square inch, and are tough enough to prevent disintegration of the binder or dislocation of the grains under impacts encountered in use but are sufficiently brittle to permit mechanical flexing in which the bond is cracked to impart flexibility to the abras'ive articles without serious injury to the bond. The coated abrasive articles made in accordance with our invention have at least one-third of the volume of the grits of the grit layer above the average level of the resinous adhesive, the bond between the grains extends under and forms a stratum between the bottoms of the grains and the backing, and a substantial portion of the backing has its thickness unpenetrated by and unmodified by the resinous adhesive. The foregoing statements apply both to the abrasive articles, described in the specific examples, and to abrasive .belts or coated fabrics of the nature of sandpaper in which the usual cellulosic backings of paper or cloth are employed in place of the steel backings of the specific examples.

As is evidenced by the examples, our method is adapted to a number of variations such as the inclusion of inert fillers. It is also, of course, possible to use different types of resin on the grains and on the backing as, for example, a glycero-phathalic anhydride type of resin can be used for either the adhesive or the coating on the grain in combination with a phenolic condensation product used for the other. Obviously, it is also possible to use a solution of a normally solid resin in a suitable solvent, instead of the liquid resin adhesive. These and other modifications are to be understood as coming within the contemplation of our invention, the scope of which is to be limited solely by the following claims.

We claim:

1. A coated abrasive article of the nature of sandpaper comprising a backing having a layer of grit bonded thereto by a tough, brittle, substantially inflexible bond consisting essentially of a heat-hardened substantially unplasticized phenol-aldehyde condensation product resin, the backing being substantially unpenetrated by and unmodified by the bond and the bond having the tensile strength, water-resistance and hardness characteristic of such resins when cured for a number of hours at a temperature of at least 250 F.

2. In the method'of making a coated abrasive article comprising a supporting backing and an abrasive surface of grits adherently united to a side thereof by a heat-hardened bond, the steps which comprise applying a coating of liquid heathardenable resinous material to a backing, applying .a coating of abrasive grains to the resin coated backing, drying the liquid resin by heating at temperatures not substantially in excess of F., and thereafter baking the article for at least six hours at temperatures of at least 250 F. to heat-harden the bond.

3. In the method of making a coated abrasive article comprising a supporting backing and an abrasive surface of grits adherently united to a side thereof by a heat-hardened bond, the steps which comprise applyin a coating of liquid phenolic condensation product resin to a backing, applying a coating of abrasive grains to the resin coated backing, drying the liquid resin by heating at temperatures not substantially in excess of 130 F., and thereafter baking the article for at least six hours at temperatures of at least 250 F. to heat-harden the bond.

4. An abrasive disc having a central arbor hole for mounting and comprising a somewhat flexible backing having sufficient rigidity and strength for mounting by means of'the arbor hole and having a substantially single layer of abrasive grain applied to the backing, and a grain-bonding coat on the backing of an unplasticized heat-hardened phenol-aldehyde resin having the strength and hardness characteristic of such resins when heat-treated for six hours at 300 F., whereby the grain is rendered very resistant to removal by the grinding stresses encountered in service.

5. In the method of making abrasive discs of the type having an arbor hole for mounting and a somewhat flexible backing having sufficient rigidity and strength for mounting by means of the arbor hole, the steps which comprise applying a coating of liquid heat-hardenable synthetic resinous material to the backing, applying a substantially single layer of abrasive grain to the resinous coated backing, drying the liquid resinous material by heating at a temperature not substantially in excess of 130 F., and thereafter baking the article for at least six hours at a temperature of at least 250 F. to heat-harden the resin.

6. In the method of making abrasive discs of the type having an arbor hole for mounting and a somewhat flexible backing having sufiicient rigidity and strength for mounting by means of the arbor hole, the steps which comprise applying a coating or" a liquid phenol-aldehyde resin to the backing, applying a substantially single layer of abrasive grain to the resin-coated backing, drying the liquid resin by heating at temperatures not substantially in excess of 130 F., and thereafter baking the article for at least six hours at temperatures of at least 250 F. to heatharden the bond.

'7. An abrasive disc having a central arbor hole and comprising a somewhat flexible cellulosic backing having suificient rigidity and strength for mounting by means of the arbor hole and having a substantially single layer of abrasive grain bonded to the backing by a layer of unplasticized phenol-aldehyde resin curedto a hard, brittle, substantially inflexible state, and having sufiicient tensile strength and toughness to prevent disintegration of the resinous bond or dislocation of the abrasive grains from the bond under impacts encountered in the use of abrasive discs, the cellulosic backing having a substan- 8 tial portion of its thickness unpenetrated by and unmodified by said resinous bond.

8. A coated abrasive article of the nature of sandpaper comprising a backing having a layer of abrasive grains attached thereto by a bond comprising two different materials, one of the said bond materials being tough, brittle and substantially inflexible and comprising essentially a heathardened substantially unplasticized phenol-aldehyde condensation product resin having the physical properties characteristic of such resin when cured for a number of hours at a temperature of at least 250 F. and the backing being substantially unpene'trated by and unmodified by the bond.

9. An abrasive disc having a central arbor hole for mounting and comprising a somewhat flexible backing having sufficient rigidity and strength for mounting by means of the arbor hole and having a substantially single layer of abrasive grains attached thereto by a bond comprising two different materials, one of the said bond materials comprising essentially a heat-hardened substantially unplasticized phenol-aldehyde 'condensation product resin having the strength and hardness characteristic of such resin when cured for a number of hours at a temperature of at least 250 F., whereby the grain is rendered very resistant to removal by the grinding stresses en countered in service.

FRANK J. TONE. HARRY C. MARTIN.

DES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number 4 Name Date 915,430 Hannah Mar. 16, 1909 1,217,593 Graft Feb. 2'7, 1917 1,626,246 Martin Apr. 26, 1927 1,775,631 Carlton Sept. 16, 1930 2,184,896 Oglesby Dec. 26, 1939 FOREIGN PATENTS Number Country Date 833,160 France July 8, 1938 

1. A COATED ABRASIVE ARTICLE OF THE NATURE OF SANDPAPER COMPRISING A BACKING HAVING A LAYER OF GRIT BONDED THERETO BY A TOUGH, BRITTLE, SUBSTANTIALLY INFLEXIBLE BOND CONSISTING ESSENTIALLY OF A HEAT-HARDENED SUBSTANTIALLY UNPLASTICIZED PHENOL-ALDEHYDE CONDENSATION PRODUCT RESIN, THE BACKING BEING SUBSTANTIALLY UNPENETRATED BY AND UNMODIFIED BY THE BOND AND THE BOND HAVING THE TENSILE STRENGTH, WATER-RESISTANCE AND HARDNESS CHARACTERISTIC OF SUCH RESINS WHEN CURED FOR A NUMBER OF HOURS AT A TEMPERATURE OF AT LEAST 250* F. 